Sync root filesystem

[rlogiacco]

I have a root filesystem on a USB hard drive (btrfs) and I wish to keep it synched with the root fs on my SD card so to have a fully functional and always up to date fallback root. I'm new to btrfs, but for what I understaood it is somehow similar to a normal ext3/4 filesystem with an intrinsic ability to chroot: this way you can have snapshots by copy.
If my understanding is not too far from reality, I believe I can keep the two filesystems in sync by using rsync from the USB drive current root to the SD card current root without bothering moving over the snapshots (to save space and write access to the SD card).

The idea is to cron schedule something like the following:

Code:

mount /dev/mmcblk0p1 /mnt/sd-root-fs
rsync -aAHXv --delete /* /mnt/sd-root-fs/@root --exclude={"/boot/*","/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*",/lost+found}
umount /mnt/sd-root-fs

Will that work? Am I completely misunderstanding btrfs?